You should treat your mortgage and any other loan secured against your home as a priority debt as you are potentially at risk of losing your home if you don't make payments.
Even if you cannot afford to pay your mortgage instalment in full you should look to pay what you can afford, even if this is just a small amount.
If you have other debts such as unsecured loans, credit cards, catalogues you should prioritise your mortgage payment over them. This link will help you identify what is and is not a priority debt (opens as a new tab).
If you have other debts that are impacting on your ability to pay your mortgage then it is important to assess your situation fully and you should seek advice to address all of your financial difficulties and options to deal with them.
If you have surplus income each month you may be able to apply for a Debt Arrangement Scheme that can include your mortgage arrears. A money adviser can talk you through the process of dealing with this.